Movement monitoring apparatus

ABSTRACT

A system for monitoring movements of a patient and indicating when the degree of movement is such as to require attention includes a scanner providing a limited movement sensitive field surrounding at least part of the patient. Circuitry monitors variations in the field caused by the patients movements and controls alarm circuitry for calling attention to the patient, for example on cessation of normal breathing or at the onset of undue restlessness in a patient to be kept quiet. The scanner is suitably a microwave radar unit.

United States Patent 1 1 Bloice MOVEMENT MONITORING APPARATUS [75]Inventor: John Anthony Bloiee, lsleworth,

England {73] Assignee: Memco (Electronics) Limited,

lsleworth, England [22] Filed: Feb. 14, 1972 [21] Appl. No.: 225,934

[30] Foreign Application Priority Data Sept. 7, 1971 Great Britain41720/71 [52] US. Cl 128/2 R, 128/2 A, l28/2.08, 340/279 [51] Int. ClA61b 5/08 [58] Field of Search 128/2 R, 2 A, 2 S, 2 N, l28/2.08;340/279, 258 A Mar. 12, 1974 Primary Examiner-Kyle L. Howell Attorney,Agent, or Firm-Robert W. Dilts; Harry G. Weissenberger; Carlisle M.Moore [5 7] ABSTRACT A system for monitoring movements of a patient andindicating when the degree of movement is such as to require attentionincludes a scanner providing a limited movement sensitive fieldsurrounding at least part of the patient. Circuitry monitors variationsin the [56] References cued field caused by the patients movements andcontrols UNITED STATES PATENTS alarm circuitry for calling attention tothe patient, for 3,547,106 12/ 1970 Bornmann 128/2 S example oncessation of normal breathing or at the 3,275,975 9/1966 King i 340/279X onset of undue restlessness in a patient to be kept 3,512,155 5/1970Blolce 340/253 A X quiet. The scanner is suitably a microwave radarunit. 3,193,823 7/1965 Laakmann 340/258 A X 3,691,558 9/1972 Hoard et a1340/258 A X 11 Claims, 7 Drawing Figures PATENTED MAR i 2 I974 SHEET 1BF 5 PATENTEI] MAR 12 1914 SHEEI 3 [IF 5 FlG.5a.

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MOVEMENT MONITORING APPARATUS tem employs a pressure-sensitive mattresson which the patient is placed, movements of the patient disturbing thepattern of flow of a pressure fluid through conduits in the mattress,such pressure variations being monitored to provide an indication of thedegree of movement of the patient. In such systems, the patient has tobe disturbed in order to commence monitoring, and

often the freedom of movement of the patient is considerably reduced. Inmany situations it may be distinctly unwise to disturb the patient, whenhis physiological condition is already critical. For example, it may beunwise to transfer a patient from an ordinary bed to one provided with apressure-sensitive mattress when his condition is such that movementcould prove damagmg.

fl'he present invention is intended to provide apparatus suitable formonitoring patients in which no physical contact with the patient isrequired, so that monitoring can be commenced at will without anydisturbance to the patient.

In accordance with the invention there is provided apparatus suitablefor monitoring movements of a patient and indicating when the degree ofmovement is such as to require attention, comprising a scanner arrangedin use to provide a movement-sensitive field enveloping at least part ofthe patient, circuitry for monitoring variations in the field, andindicator circuitry controlled by the monitoring circuitry to providethe indication that attention to the patient is required.

The monitor system thus operates on a principle which may be called thefield disturbance principle in which a steady electro-magnetic field, isset up in a region to be kept under surveillance, and the disturbancesin the field caused by movement therein are monitored.

This principle is used in microwave intruder detection systems, such asthose described in U.S. Pat. No. 3,512,155 and U.S. Pat. No. 3,691,556,both of which are assigned to the same assignee as is this applicationand, the contents of which are hereby inserted in this application byreference.

The scanner of the present monitoring system is suitably one of themicrowave radar scanners described in these two U.S. patents with themonitor circuitry thereof modified in accordance with the teaching ofthis invention.

In U.S. Pat. No. 3,512,155 the radar unit consists of a transmitter andreceiver and operates on the Doppler principle. A beam is transmittedand reflections from objects in the beam path return to the receiver. Inthe absence of movement in this field, there is no frequency differencein the transmitted and reflected signals. When movement occurs in thefield, however a frequency change or Doppler shift occurs, and this ismonitored to provide an indication of movements in the field ofsurveillance. In U.S. Pat. No. 3,691,556 the radar unit is a transmitteronly and movements in the field of surveillance dusturb the patternradiated and cause load impedance variations at the transmitter. Theseare monitored by an auxiliary oscillator circuit to provide the movementindicator.

The apparatus of this invention is particularly, but not exclusively,suitable for use as a respiration monitor or apnea detector, registeringthe patients respiration by means of the movements of the chest wall.Apnea is the cessation of respiration and is a common condition inpremature babies (Apnea Neonatorum). Provided apnea is detected quicklyenough, it is generally possible to restimulate respiration.

The detection of apnea is achieved by reversing the role of the intruderdetector, in that an alarm is given in the absence of movement asopposed to the appearance of movement in the field of surveillance. Inaddition, by suitably modifying the circuit values of the intruderdetector circuitry, sensitivity to people in the near vicinity of thepatient being monitored can be greatly reduced.

The monitoring system will now be described in more detail, by way ofexample only, and with reference to the accompanying diagrammaticdrawings, in which:

FIG. 1 is a plan view of the scanner of the monitoring system as usedfor monitoring the respiration of babies in an infant ward;

FIG. 2 is an elevation of the scanner;

FIG. 3 is a plan view of the scanner in use in an adult ward, showingtwo possible positions of the scanner;

FIG. 4 shows the two possible positions of the scanner in elevation;

FIG. 5 covers two sheets of drawing designated FIG. 5a and FIG. 5b,respectively, and shows the monitor circuitry of the system; and

FIG. 6 shows the system power supply and indicator circuitry in the formof an alarm.

Referring to FIG. 1 and 2, the scanner 1 is mounted for pivotal movementabout a vertical axis at the free end of a horizontal arm 2 pivoted to awall as at 3. The scanner is downwardly directed. The mounting at 3provides for adjustment of the height of the scanner 1 above the floor.

As shown in FIG. 1, as many scanners 1 may be provided in an infant wardas is appropriate to the capacity of the ward. It will be appreciatedthat it is unlikely that all babies in the infant ward will require tobe monitored at any particular time, unless the ward is specialized tothe care of such infants.

The infants 4 to be monitored are placed in cots or incubators 5 beneaththe respective scanners l. The scanners are arranged to provide aradiation pattern whose shape is as shown by the dotted outline 6 inFIG. I. It will be seen that this outline is generally elliptical, andthe scanner 1 is preferably arranged so that the longer axis of theellipse lies along the length of the infants body.

It will be seen from FIG. 1 that the mounting of the scanners 1 on thehorizontal arms 2 allows for the cots or incubators 5 to be situated invarious positions, and any particular scanner can be hinged away againstthe wall when not in use, as shown in dotted outline in the centralsketch of FIG. 1, so as to take up less room.

The scanner 1 may be as described in our US. Pat. No. 3,5 l 2, l 55.This particular form of scanner is a twoaerial doppler device employinginteraerial coupling to feed microwave energy from the transmitter horndirectly to the receiver horn.

Microwave radiation from the transmitter horn is reflected from. forexample, the moving chest wall of the patient to the receiver horn. Thefrequency of the reflected radiation is varied because of the movementof the chest wall, and the difference in frequency between thetransmitted and received waves is seen after amplification as a signalvoltage of one cycle for every half wavelength of relative movement. Theparticular scanner' under discussion operates at a transmissionwavelength of 3cm, so that the signal voltage is of one cycle for everyl.5cm of chest movement.

If the respiratory excursion of the chest wall is considerably greaterthan l.5cm, several cycles of doppler signal will be generated.According to the teaching of this invention the signal is rectified andsmoothed in such a way that a resulting signal is produced representingthe instantaneous velocity of the chest wall at any point of therespiratory cycle. If this signal voltage falls below a certain leveland this condition persists for longer than a preselected interval, analarm sounds to indicate cessation of breathing. During this interval,an adequate movement on the part of the patient restores the instrumentto its normal operating mode, cancelling the alarm. Movement by thepatient once the alarm is sounding also has the effect of cancelling thealarm. These processes will shortly be described in more detail.

If the chest wall movement is less than l.5cm, a useful output signalwill still be generated as a result of the phase shift of the reflectedsignal.

It has been found that this type of scanner will operate effectivelywithout the inter-aerial coupling. At the short ranges involved in thepatient-monitoring application, the intensity of the reflected signalvaries with the chest position to a sufficient extent to provideefficient monitoring.

The maximum microwave energy level at the transmitter antenna apertureis 50 ,uW per cm Legs 5cm in length have been added to the front of thescanner so that it cannot be brought closer than 5cm to a patient, andat this distance from the antenna aperture the maximum energy leveldrops to pW per cm. A minimum working distance of one foot isrecommended for infant-monitoring applications, at which distance theenergy level is only 1 ,uW per cm This is below the upper permissiblelevel for this frequency range by a factor of thousands. With adults,because of the large amplitude of chest movement, satisfactory operationis obtained with the unit some 3 or 4 feet from the chest wall.

FIG. 3 shows two positions of the scanner for monitoring an adultpatient.

In the left-hand sketch the scanner is near the foot of the bed anddirects a fan-shaped radiation curtain giving wide coverage of thepatients head and shoulder region. In the right-hand sketch, the scanneris placed directly above the patients chest and directed downwardly, toprovide a radiation pattern similar to that used for monitoring infants.The coverage provided is more narrow, but monitoring is more sensitivewith the scanner in the position shown in the right-hand sketch.

FIG. 4 shows these two positions of the scanner in elevation, indicatingthe height adjustment facility provided by the scanners support.

FIG. 5 (appearing on two sheets of drawing designated 5a and 5b) showsthe monitor circuitry.

The receiver diode D11 is located in the receiver aerial, and has itscathode connected to the aerial which is grounded. Its anode isconnected to ground through a decoupling capacitance and through anelectrolytic capacitance C i. This is shunted by a pre-set potentiometerVRll with which the response range of the circuitry may be adjusted andwhose adjustable center tap is connected through an electrolyticcapacitance C3 to the input 1 of an amplifier A1. A supply connection 2of the amplifier Al is connected to ground through an electrolyticcapacitance C2 and to a supply terminal Pl3 through a resistance R2. Theamplifier output 3 is connected to the terminal P13 through a resistanceR5. It is also connected to ground through the seriesconnectedcombination of a resistance R6 and an electrolytic capacitance C4. Thejunction of resistance R6 and capacitance C4 is connected to theamplifier input 1 through a feedback resistance R4. The seriesconnectedcombination of resistance R6 and capacitance C4 is shunted by anelectrolytic capacitance C5.

The amplifiers output 3 is connected through an electrolytic capacitanceC6 to the base of a first NPN transistor VTll. The base of thistransistor is also connected to the cathode of a diode D3 whose anode isconnected to earth. The emitter of transistor VTl is connected to groundand its collector to a terminal P12 through a resistance R7. Thecollector is also connected to ground through an electrolyticcapacitance C7, and to the anode of a diode D6. The cathode of the diodeD6 is connected to a terminal PM. The components so far described, withthe exception of the receiver aerial, receiver diode and its decouplingcapacitance, and the pre-set potentiometer VRll are mounted on a firstprinted circuit board.

A terminal 1P2 on a second printed circuit board is linked to terminalPM on the first board. Terminal P2 is connected to the base of a secondNPN transistor VTZ. The emitter of this transistor is connected toground. Its collector is connected to its base through theseries-connected combination of a resistance R9 and an electrolyticcapacitance C8. The junction of the resistance R9 and the capacitance C8is connected to one end of the energisation winding of a relay RLl. Theother end of the energisation winding is connected to a terminal P7 towhich is connected one end of a resistance R3 whose other end isconnected to the cathode of a Zener diode ZDZ. The anode of this Zenerdiode is connected to earth. The cathode is also connected to a terminalP8, which is linked to terminal Pll3 on the first printed circuit board.

Terminal P7 is connected to the cathode of a diode D5 whose anode isconnected to ground. The cathode is also connected to the collector of athird NPN transistor VT3, this collector being connected to the basethrough a resistance RM).

The base of transistor VT3 is connected to the cathode of a Zener diodeZ04 whose anode is connected to ground. The cathode is also connectedthrough the series-connected combination of resistances R111 and R12 tothat end of the potentiometer VRll which is not grounded. The junctionof those resistances R111 and R12 is connected to ground through anelectrolytic capacitance C11. The Zener diode ZD4 is shunted by anelectrolytic capacitance C9.

The emitter of transistor VT3 is connected to ground through acapacitance C and to the cathode of the Gunn diode GDl of thetransmitter aerial. The anode of the Gunn diode GD]. is connected to theaerial and to ground. The diode is shunted by a capacitance C12.

The contacts of relay RL1 are connected to terminals P9 and P10. Theseare connected to ground through respective capacitances C13 and C14.

Terminal P7 is linked to terminal P12 on the first printed circuit boardand is connected to ground through a fuse PS1 and a capacitance C15.

Terminal P9 is connected through a lamp shunted by a Zener diode ZD7 toan output terminal labelled GRN.

Terminal P10 is connected to an output labelled BLUE, which is connectedto ground.

The junction of fuse PS1 and capacitance C is connected to an outputlabelled RED.

Referring to FIG. 6, a main transformer T1 has its primary windingconnected to the AC main supply. The primary winding is center-tapped toprovide for dualvoltage operation, a voltage selector switch beingprovided as shown.

The transformer secondary winding provides l2 volts AC which isrectified by a bridge rectifier comprising diodes D64 to D67. Therectifier output is smoothed by a resistance R64 and capacitance C65.The smoothed output across capacitance C65 is applied to inputs labelledRED and BLUE, connected to the similarly labelled outputs of thecircuitry of FIG. 5.

A lamp L1 is connected between the input labelled RED and an inputlabelled GREEN which is connected to the output labelled GRN of thecircuitry of HG. 5. A lmA drive is available from a pair of terminals,one of which is connected to the input labelled RED and the other whichis connected through a resistance R1 to the input labelled GREEN.

The input labelled GREEN is connected through an electrolyticcapacitance C61 to the cathode of a diode C61 whose anode is connectedto the input labelled BLUE. It will be recalled that the similarlylabelled output of the circuitry of FIG. 5 is connected to ground. Thecathode of the diode D61 is connected to the anode of a diode D62 whosecathode is connected to earth through a resistance R62. The resistanceR62 is shunted by a selected one of three electrolytic capacitances C62,C63 and C64.

The cathode of diode D62 is also connected through a resistance R63 tothe base of an NPN transistor VT61 whose emitter is connected to ground.Its collector is connected to one end of the energisation winding of arelay RL61, the other end of this winding being connected to theunsmoothed supply through a switch SW1. The energisation winding isshunted by a diode D63 whose anode is connected to the collector oftransistor VT61.

That end of the energisation winding remote from transistor VT61 isconnected through a noise generator to one of the relay RL61 contacts,the other of which is connected to ground.

The operation of the circuitry will now be described with reference toFIGS. 5 and 6.

It will be recalled that the Doppler frequency shift is seen, afteramplification, as a voltage. This voltage is the output voltage ofamplifier A1. The amplifier A1 is frequency selective, and is tuned toan optimum frequency by means of the feedback resistance R4 andassociated component values. It has been found that the optimum responsefrequency for monitoring of respiration is 11-12.

The output voltage of the amplifier Al is applied to the capacitance C7,which acts as a store, through the pump circuit provided by transistorVTl. The voltage across capacitance C7 is applied to the base oftransistor VT2 which acts as a relay driver.

So long as the voltage across capacitance C7 exceeds a preselectedvalue, the relay RL1 is kept energised, and the normally closed contactsconnected between terminals P9 and P10 are open.

A circuit may be traced from one pole of the smoothed supply, that isone plate of capacitance C65, through lamp L1, the lamp shunted by Zenerdiode ZD7, the contacts of relay RL1, to the other pole of the smoothedsupply, that is the other plate of capacitance C65.

Thus, so long as the Doppler output voltage exceeds a predeterminedvalue, and the relay contacts are held open, these two lamps are notlit.

If this voltage falls below that level, the voltage at the base oftransistor VT2 drops to such an extent that the relay RL1 drops out. Thenormally closed contacts therefore close to complete the lampenergisation circuit, and both lamps therefore glow.

Lamp L1 is situated at an alarm station remote from the scanner and theother lamp is situated on the scanner, but appropriately situated so asto be invisible to the patient being monitored.

As the patient breathes, the voltage across capacitance C7 continuallyvaries, passing above and below the limit value at the respiration rate,The two lamps consequently blink on and off at the same rate.

The sensitivity may be adjusted by means of potentiometer VRl so that ifthe degree of chest excursion falls below a particular amount, moreparticularly if breathing stops altogether, the relay RL1 is no longerenergised, the normally closed contacts remaining continuously closed.Consequently both lamps shine continuously.

While the patient was breathing normally, the intermittent operation ofthe relay RL1 was supplying pulses to the GREEN input of the alarmcircuitry. These passed through diode D62, negative pulses being shuntedto ground by diode D61, to be aggregated in the selected one of thecapacitances C62, C63 and C64. The selected capacitance is maintainedcharged by these pulses, so that transistor VT61 remains conducting. Therelay RL61 driven by this transistor therefore remains energised, andits contacts are held open to inhibit operation of the noise generator.

When relay RL1 becomes continuously de-energised, activating thecontacts thereof, on cessation of breathing, no further pulses reach theselected one of capacitances C62, C63 and C64, which thereforedischarges through resistance R62. The values of capacitances C62, C63and C64 are chosen to give respective delay times of 10, 20 and 30seconds. The result is that 10, 20 or 30 seconds after relay RL1 becomescontinuously de-energised, activating the contacts thereof, the voltageon the base of transistor VT61 drops below a limit value, the relay RL61is de-energised and its contacts close to activate the noise generatorto sound an alarm.

It will be appreciated that for the alarm circuitry to operate theswitch SW1 must be closed. The function of the switch will be describedshortly.

The transistor VT3 is a series-current regulator for the Gunn diode GDl.The capacitances C13, C14 and C15 decouple any RF present at terminalsPQ, PM) or P7, due for example to X-ray equipment operating in thevicinity of the monitor.

The Zener diode ZD7 shunting the second lamp is intended to maintaincircuit continuity in the event of lamp failure.

Should the lamp Ll fail the selected capacitance C62, C63 or C64discharges to sound the alarm. in the event of failure of the radardevices or the amplifier Al, both relays will open to sound the alarm.The device will become inoperative if there is a failure of the mainsupply, but provision could be made to keep the unit operating for a fewhours from a 12 volt battery.

The lmA drive terminals may be connected to a recording instrument suchas a chart recorder, to provide a permanent record of the patientsrespiration. As well as providing a suitable pulse record of therespiration rate, it is envisaged that the output of the amplifier A1must be brought out to an external connection from which a record of therespiration waveform could be obtained. Heart-beat waveforms are ofgreat assistance in diagnosing various forms of cardiac complaint, andit is thought that respiration waveforms might provide similarly usefulinformation regarding respiratory complaints.

If the instrument has been disconnected from the main supply for sometime a warm-up" period of about 3 minutes is required before it willfunction. This is because of the long time constant circuits employed inthe apparatus. If the switch SW1 is closed during this period, thedetector will remain insensitive to movement, the monitor lamps willglow continuously, and the alarm will sound. As this will be ratherinconvenient, the switch SW1 is opened while the unit is allowed to warmup, so disabling the alarm circuit. When the warm-up period is complete,the detector becomes sensitive to movement, the monitor lamps begin toblink at the respiration rate, and the switch may be closed to ready thealarm. This warm-up period may be obviated by keeping the instrumentpermanently connected to the main supply, switch SW1 being held openuntil the unit is required for use.

When the unit is to be used, the detector is positioned so as to observethe patients respiratory movements, the appropriate alarm delay time of10, or seconds is selected, and the detector is adjusted for optimalsensitivity.

A delay time of 10 seconds has been found to be the most appropriate fordetecting apnea in infants, but longer periods may be used for adults,depending on the illness or complaint concerned.

Optimal sensitivity is obtained by gradually advancing the detectorsensitivity control from a minimum position, while observing the monitorlamps. The optimal setting is considered to be that in which the on andoff phases ofthe monitor lamps are of approximately equal duration. Ifsensitivity is too low, the lamps will be on most, or all of the time,If the sensitivity is too high. the lamps will be off most or all of thetime, and with too low sensitivity the instrument is liable to give analarm even when breathing is only shallower than normal. If sensitivityis too high, however, there will be a great risk of extraneous movementsin the vicinity of the patient exciting the instrument.

The sensitivity setting required will depend on the distance between thedetector and the patient, the amplitude and frequency of breathing, andthe presence of an interposed material, such as the roof of an incubatorin the case of premature babies. In all cases, sensitivity should beheld low as possible whilst compatible with detecting respiration.

The instrument has been made rather insensitive to movements atfrequencies higher than those likely to be encountered in breathing,that is to say of the order of cycles per minute. This lessens thelikelihood of the device being activated by movements extraneous to thepatient.

it should be noted that a large amplitude movement by the patient willparalyse the circuitry for l or 2 seconds, rendering it temporarilyinsensitive to respiratory movement. Consequently, the instrument cannotbe relied upon for an entirely accurate record of the respiratory rate,as such record is liable to be frequently interrupted by a restlesspatient. Of course, if a record of the degree of restlessness of thepatient is required, this factor is of considerable usefulness.

The apparatus can moreover, be adapted to give the alarm if the patientis unduly restless.

The alarm is given when there is insufficient movement in the field whena signal voltage drops below a threshold (in FIG. 6 when capacitanceC62, C63 or C64 becomes sufficiently discharged). By arranging that thealarm is given when the voltage exceeds a further and higher threshold,the undue restlessness indication may be given.

The system has been used to monitor respiration in several normalnewborn infants. In each case the scanner was arranged approximately 1foot above the baby, and tests were made with the long axis bothparalled to and perpendicular to the babys height. Better results wereobtained in the latter case. The alarm signal was duly given when oneinfant subject to periodic breathing suffered apnea lasting more than 10seconds. The alarm is also given when, to test the instrument, theinfant was removed from the cot. The presence of persons standing withina foot or two of the cot did not appear to interfere with the operationof the detector, provided that its sensitivity was appropriatelyregulated.

Newborn infants in incubators have also been monitored with the device,the detector being held approximately 5cm above the upper surface of theincubator. The alarm signal was given reliably in the case of twopremature babies subject to frequent attacks of apnea. A third infantwas not subject to apnea but had shallow breathing at a rate ofapproximately 60 cycles per minute. The monitor lamps flashed at a rateclosely corresponding to this. The alarm duly sounded with the scannersituated over an empty incubator, even with persons standing closeby.

It is considered that the detector should not be placed against the sidewall of an incubator, since the infant may come close to this wall andthereby increase the energy level received, and the detector is thenliable to be activated by reflections from individuals standing close tothat side of the incubator.

Tests have been carried out on adult patients in a normally crowdedhospital ward, with the scanner situated in both positions illustratedin FIGS. 3 and 4. The

alarm was duly given when the patient held his breath and otherwiseremained motionless. The presence of staff along the side of the bed andof patients in adjacent beds caused no interference in operation.

The instrument conveniently consists of two units, the wall mounted orfree-standing scanner and the alarm unit. The scanner is connected tothe alarm unit by a cable carrying the l2 volts supply and the alarm andmonitor lamp signals. This cable need only have three cores, linking theGREEN, RED and BLUE terminals of the circuits of FIGS. 5 and 6.

The alarm unit may be placed adjacent or remote from the patient. Whereit is located adjacent the patient, it may be advantageous to set up aslave alarm at a remote station.

The instrument is simple to operate, and can be arranged as a permanentmonitoring station to which patients to be monitored are brought. Wherethe patients cannot be moved, portable scanners on free-standingsupports may be used.

No apparatus need be attached to the patient, and neither the patientnor his bed need be especially prepared for monitoring to begin. Theinconveniences which may arise if monitoring apparatus has to beattached to or otherwise placed in contact with the patient areeliminated. These inconveniences include restriction of breathing orother movement, skin irritation, accidental disconnection of links, andinterference with normal medical care. As the apparatus is not incontact with the patient, it requires no special cleaning orsterilisation. The scanner may be quickly moved to one side of there isurgent need for access to a patient, for example an infant in anincubator subject to apnea.

As has already been mentioned, the energy level at the patient isreduced to an extremely small value which is below that regarded as theupper permissible level by a factor of thousands.

It is not thought that the instrument will interfere with the taking ofECG records, in view of the high frequency used.

The instrument may find extensive applications in labor wards, inspecial neonatal units, and in childrens wards. It may also be useful incasualty cubicles, in adult medical and surgical wards, in anaestheticor recovery rooms. it will be used for monitoring patients sufferingfrom drug overdose, or head injuries, and for monitoring patients onrespirators to ensure that there is actually movement of the chest. Theinstrument will be of particular assistance in monitoring patients inside rooms or private wards where close nursing supervision may bedifficult.

I claim:

1. Movement monitoring apparatus comprising:

a. microwave radar means providing a limited movement-sensitive field ofmicrowave radiation;

b. monitor circuit means monitoring disturbances of said field andproviding at its output a pulsed signal indicative of the degree offield disturbance;

c. aggregating circuit means coupled to the output of said monitorcircuit means to aggregate said pulsed signal to provide at its output asignal voltage the level of which is indicative of said degree of fielddisturbance;

d. threshold circuit means defining a predetermined threshold voltageand coupled to the output of said aggregating circuit means to receivesaid signal voltage;

e. trigger circuit means coupled to the output of said threshold circuitmeans to be activated thereby when said signal voltage is below saidpredetermined threshold voltage;

f. delay circuit means coupled to the output of said trigger circuitmeans and providing a predetermined delay between the appearance at itsinput of an input signal caused by activation of said trigger circuitmeans and the appearance at its output of a corresponding output signal;and

g. alarm circuit means connected to the output of said delay circuit andactivated by said output signal thereof.

2. Apparatus as set forth in claim 1, in which said microwave radarmeans is a doppler radar unit and said pulsed signal is indicative ofthe doppler frequency shift in the output signal of said unit.

3. Apparatus as set forth in claim 1, in which said microwave radarmeans is a microwave radar transmitter and said pulsed signal isindicative of variations in the impedance loading of said transmitterdue to said field disturbances.

4. Apparatus as set forth in claim 1, in which said monitor circuitmeans includes a filter which responds only to frequencies lower than apredetermined upper limit, whereby said pulsed signal is not indicativeof field disturbances at frequencies above said upper limit.

5. Apparatus as set forth in claim 4, in which said upper frequencylimit is Hz.

6. Apparatus as set forth in claim 1, in which said trigger circuitmeans includes terminals for connection to a recording instrument toprovide thereto said voltage signal, whereby a record of the degree offield disturbance may be obtained.

7. Apparatus as set forth in claim 1 wherein said trigger circuit meansand said alarm circuit means include means for returning to theirde-activated state when said signal voltage is returned to saidthreshold voltage.

8. Apparatus as set forth in claim 1 including means wherein said alarmcircuit means is activated by failure of said other means thereof.

9. Apparatus as set forth in claim 4 constructed as respirationmonitoring apparatus including means wherein said field is adapted toenvelop at least the chest of a patient; said predetermined thresholdvoltage is produced by normal respiration of said patient, and saidupper limit of frequencies corresponds to movements of the chest wall ofsaid patient characteristic of normal respiration.

10. Apparatus as set forth in claim 1 wherein said alarm circuitincludes a switch means for deactivation thereof.

1 1. Apparatus as claimed in claim 1 including means wherein saidpredetermined delay provided by said delay circuit means is restored toits full value upon disappearance of said input signal at said input ofsaid delay circuit means.

1. Movement monitoring apparatus comprising: a. microwave radar meansproviding a limited movement-sensitive field of microwave radiation; b.monitor circuit means monitoring disturbances of said field andproviding at its output a pulsed signal indicative of the degree offield disturbance; Pg,22 c. aggregating circuit means coupled to theoutput of said monitor circuit means to aggregate said pulsed signal toprovide at its output a signal voltage the level of which is indicativeof said degree of field disturbance; d. threshold circuit means defininga predetermined threshold voltage and coupled to the output of saidaggregating circuit means to receive said signal voltage; e. triggercircuit means coupled to the output of said threshold circuit means tobe activated thereby when said signal voltage is below saidpredetermined threshold voltage; f. delay circuit means coupled to theoutput of said trigger circuit means and providing a predetermined delaybetween the appearance at its input of an input signal caused byactivation of said trigger circuit means and the appearance at itsoutput of a corresponding output signal; and g. alarm circuit meansconnected to the output of said delay circuit and activated by saidoutput signal thereof.
 2. Apparatus as set forth in claim 1, in whichsaid microwave radar means is a doppler radar unit and said pulsedsignal is indicative of the doppler frequency shift in the output signalof said unit.
 3. Apparatus as set forth in claim 1, in which saidmicrowave radar means is a microwave radar transmitter and said pulsedsignal is indicative of variations in the impedance loading of saidtransmitter due to said field disturbances.
 4. Apparatus as set forth inclaim 1, in which said monitor circuit means includes a filter whichresponds only to frequencies lower than a predetermined upper limit,whereby said pulsed signal is not indicative of field disturbances atfrequencies above said upper limit.
 5. Apparatus as set forth in claim4, in which said upper frequency limit is 80 Hz.
 6. Apparatus as setforth in claim 1, in which said trigger circuit means includes terminalsfor connection to a recording instrument to provide thereto said voltagesignal, whereby a record of the degree of field disturbance may beobtained.
 7. Apparatus as set forth in claim 1 wherein said triggercircuit means and said alarm circuit means include means for returningto their de-activated state when said signal voltage is returned to saidthreshold voltage.
 8. Apparatus as set forth in claim 1 including meanswherein said alarm circuit means is activated by failure of said othermeans thereof.
 9. Apparatus as set forth in claim 4 constructed asrespiration monitoring apparatus including means wherein said field isadapted to envelop at least the chest of a patient; said predeterminedthreshold voltage is produced by normal respiration of said patient, andsaid upper limit of frequencies corresponds to movements of the chestwall of said patient characteristic of normal respiration.
 10. Apparatusas set forth in claim 1 wherein said alarm circuit includes a switchmeans for deactivation thereof.
 11. Apparatus as claimed in claim 1including means wherein said predetermined delay provided by said delaycircuit means is restored to its full value upon disappearance of saidinput signal at said input of said delay circuit means.